Mould
Dust or mould building up on the paint.
Causes
- Insufficient care during surface preparation
- Moisture entering through cracks
- Sea sand used in the wall mortar
Solution
If moisture is the cause, eliminate the source; repair the roof if needed. Fill any cracks with cement-based exterior mortar and review the indoor ventilation system. Brush off dust and other residue, wash the surface with water and let it dry, then prime it and repaint with a quality silicone-based paint.